Elsevier

Nutrition

Volume 31, Issues 7–8, July–August 2015, Pages 916-922
Nutrition

Review
Exercise and oxidative stress: Potential effects of antioxidant dietary strategies in sports

https://doi.org/10.1016/j.nut.2015.02.005Get rights and content

Highlights

  • Antioxidant supplementation has spread to reduce and sometimes prevent oxidative stress in sport practitioners.

  • Antioxidant supplementation may be detrimental for exercise-related oxidative stress in some cases.

  • A diet rich in fruits and vegetables is likely the best tool to prevent or reduce oxidative stress.

  • A personalized plan according to the specific requirement of the athlete is advocated.

Abstract

Free radicals are produced during aerobic cellular metabolism and have key roles as regulatory mediators in signaling processes. Oxidative stress reflects an imbalance between production of reactive oxygen species and an adequate antioxidant defense. This adverse condition may lead to cellular and tissue damage of components, and is involved in different physiopathological states, including aging, exercise, inflammatory, cardiovascular and neurodegenerative diseases, and cancer. In particular, the relationship between exercise and oxidative stress is extremely complex, depending on the mode, intensity, and duration of exercise. Regular moderate training appears beneficial for oxidative stress and health. Conversely, acute exercise leads to increased oxidative stress, although this same stimulus is necessary to allow an up-regulation in endogenous antioxidant defenses (hormesis). Supporting endogenous defenses with additional oral antioxidant supplementation may represent a suitable noninvasive tool for preventing or reducing oxidative stress during training. However, excess of exogenous antioxidants may have detrimental effects on health and performance. Whole foods, rather than capsules, contain antioxidants in natural ratios and proportions, which may act in synergy to optimize the antioxidant effect. Thus, an adequate intake of vitamins and minerals through a varied and balanced diet remains the best approach to maintain an optimal antioxidant status. Antioxidant supplementation may be warranted in particular conditions, when athletes are exposed to high oxidative stress or fail to meet dietary antioxidant requirements. Aim of this review is to discuss the evidence on the relationship between exercise and oxidative stress, and the potential effects of dietary strategies in athletes. The differences between diet and exogenous supplementation as well as available tools to estimate effectiveness of antioxidant intake are also reported. Finally, we advocate the need to adopt an individualized diet for each athlete performing a specific sport or in a specific period of training, clinically supervised with inclusion of blood analysis and physiological tests, in a comprehensive nutritional assessment.

Introduction

Oxidative stress reflects an imbalance between production of reactive oxygen species (ROS) and the ability to detoxify reactive intermediates or to repair the resulting damage by an adequate antioxidant defense. This adverse condition may lead to damage of all cellular components, including proteins, lipids, carbohydrates, and nucleic acids [1]. Oxidative stress is recognized to be involved in many physiological conditions (e.g., aging and exercise) and diseases (including inflammation, cardiovascular and neurodegenerative diseases, and cancer) [1]. In particular, the effect of exercise on redox balance is extremely complex, depending on age, sex, and training level, as well as intensity and duration of exercise. Although regular moderate training appears beneficial for oxidative stress and health, acute and strenuous bouts of aerobic and anaerobic exercise can induce ROS overproduction. Nonetheless, although exercise leads to increased oxidative stress, the same exercise stimulus appears necessary to allow an up-regulation in endogenous antioxidant defenses according to the hormesis theory (Fig. 1). Specifically, this hypothesis suggests that the organism’s reaction to repeated increases in ROS production via exercise bouts involves adaptive mechanisms. In particular, hormesis elicits an antioxidant up-regulation, a shift toward a more reducing environment, induction of increased stress resistance, ultimately leading to an enhanced life span [2]. Same adaptative responses and the detoxifying function of antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], glutathione reductase, glutathione-S-transferase) and nonenzymatic antioxidants (such as vitamins E, A, C; glutathione [GSH]; and uric acid) take part in the prevention of excessive oxidative stress related to performance enhancement, aging prevention, and pathological risk in professional athletes [2].

In recent years, the consumption of supplemental antioxidants in athletes has increased enormously despite the unclear evidence of their benefit. The delicate balance between oxidants and antioxidants may be counterbalanced by an adequate dietary/supplemental antioxidant intake (extrinsic factor). In particular, exogenous supplemental antioxidants have received interest as a noninvasive tool useful in decreasing muscle damage and improving exercise performance and in preventing or reducing oxidative stress, improving life span and performance, and lowering specific risks for pathologic outcomes that strenuous exercise produces in athletes [3], [4]. Nonetheless, the revision of available information has evidenced a lack of consistent data regarding exogenous antioxidant supplementation effects on physiological parameters, with most studies reporting no or negative effects on these end points [3], [4]. Moreover, some studies suggest adverse effects of antioxidant supplementation on the health and performance of exercise-trained individuals [3], [4]. In particular, a too-low oxidative stress status may be detrimental and may blunt positive responses related to hormesis because ROS retain key roles as regulatory mediators in signaling processes essential to the correct functioning of cells. Conversely, high doses of antioxidants may negatively affect important ROS-mediated physiological processes because they may shift from antioxidant capacity to prooxidant effects.

At present, few studies if any approach this topic from a whole food or dietary perspective [5], [6], [7], [8], [9]. An adequate intake of vitamins and minerals, and the use of natural foods that are rich in antioxidants (fruits, vegetables, etc.) through a varied and balanced diet rich in fruits, fiber, and vegetables could represent the ideal approach to maintaining the optimal antioxidant status as antioxidants are present in natural ratios and proportions, which may act in synergy to optimize the antioxidant effect. The Mediterranean diet could be a suitable candidate, although data in this field are still scarce. In this review, evidence on the relationship between exercise and oxidative stress and potential effects of dietary strategies in athletes are discussed. The differences between diet and exogenous supplementation as well as available tools to estimate effectiveness of antioxidant intake are also reported.

Section snippets

Available biomarkers to estimate oxidative stress status

The measurement of the oxidative stress in vivo is difficult due to the extreme complexity of the antioxidant/oxidant network and the very short half-life of free radicals [2]. Generally, indirect biomarkers are measured, such as conjugated dienes, hydroperoxides, malondialdehyde, 4-hydroxynonenal, hydrocarbons such as pentane and ethane (in breath), F2-isoprostanes, and oxidized low-density lipoprotein [1], [2]. Conversely, total antioxidant capacity [TAC] can be estimated in biological fluids

Effects of exercise on oxidative stress and health

At rest, oxidative stress status is generally found to be lower in athletes than in sedentary individuals, although it also has been observed increased or unchanged [11], [12]. Many variables clearly affect these results, two of the most important being differences in experimental design (e.g., exercise intensities) and different methods used to estimate oxidative stress status. Several studies showed a lower oxidative response in athletes than in controls both at rest and soon after exercise,

Dietary versus supplemental antioxidants: same effectiveness?

In the past, antioxidant supplementation was expected to be effective against cumulative effects of strenuous exercise–induced free radical damage to heart and skeletal muscle [21]. Vitamin C at various dosages, administered alone or in combination with other antioxidants, chronically or acutely, is the most frequently used antioxidant in human and experimental studies, although with discordant results on its protective role [22]. One of the key determinants for these differences is the dose

Dietary strategies and oxidative stress in athletes

Most studies concerning the area of recovery from exercise in athletes focus on the use of nutritional supplements rather than on foods [2]. The study of the effects of natural food is difficult because food products are difficult to group according to the type and content of antioxidants. Nonetheless, the protective effect of a diet containing natural sources of antioxidants is probably not equivalent to the protective effect of supplementation. Whole foods, rather than capsules, contain

Conclusions

The interrelationship of exercise and oxidative stress remains extremely complex, depending on the mode, intensity, and duration of exercise, and individual susceptibility to oxidative stress injury determined by genetic and lifestyle factors.

At present, interpretation of available results remains difficult due to the variety of physiological networks involved, and differences in biomarkers and methods used as well as in nutritional composition of foods. The development of integrative panels

Acknowledgment

The authors acknowledge Rossella Pucci for her graphical contribution to Figure 3.

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    All authors have read and approved the final manuscript version. The authors have no conflicts of interest to disclose.

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